Environmental conditions may affect materials used to make vehicles and other types of structures intended for outdoor use or for use in extreme environments, such as aerospace structures that experience dynamic and various environmental changes throughout their service history (i.e., dry to wet, cold to hot). Environmental testing of such materials at less than 0° F. and greater than 100° F., and from 0-100% humidity, is desired to identify, quantify and monitor the properties of such materials before, during and/or after one or more uses to determine if any damage to the materials has occurred.
One type of sensor that has been used for environmental testing, acoustic emission (or AE) sensors, interprets the radiation of acoustic (or elastic) waves in solid materials into usable AE waveforms that help understand how the materials behave. Such acoustic (or elastic) waves occur when a material undergoes changes in its internal structure, for example as a result of crack formation or plastic deformation due to aging, temperature gradients or external mechanical forces. The waves generated by sources of acoustic emission are of practical interest in the fields of structural health monitoring, quality control, system feedback, process monitoring, analysis validation, and others, and may be used to detect, locate and characterize damage to the material. Acoustic emission sensors are therefore useful for detecting flaws and failures in materials and structures, and determining how to apply remedial solutions and repairs to resolve structural issues. In the aerospace field, acoustic emission sensing has been identified as a technology that can be scaled for enhanced fleet inspection from the laboratory setting, to the depot and to field applications. The focus is driven by the need to identify the existence of damage as a function of service hours for the fleet in order to make critical decisions regarding remaining life.
Acoustic emission sensors have been used to monitor aerospace and other structures. Traditional approaches for attaching acoustic emission sensors to the structure to be tested include using hot glue or magnetic clamping fixtures. Many commercially available holders for acoustic emission sensors are magnetic because acoustic emission has predominantly been done on metallic surfaces. Such magnetic holders will not function with non-metallic and non-magnetic composite materials. Hot glue does not have universal application, and does not work during environmental testing at temperatures less than −65° F. and greater than 160° F. due to poor surface adhesion. Another solution has been to permanently attach acoustic emission sensors to a test article, but this approach is not feasible when testing large numbers of test articles due to expense and extended dwell time (greater than 10 hours per sensor) for curing an adhesive to affix the sensors to the test article.
Non-metallic and non-magnetic materials, such as composite materials, are now used in the manufacture of a wide variety of structures due to their high strength and rigidity, low weight, corrosion resistance and other favorable properties. For example, composite materials have become widely used to manufacture aerospace structures and component parts for aerospace structures such as aircraft ribs, spars, panels, fuselages, wings, wing boxes, fuel tanks, tail assemblies and other component parts of an aircraft because they are lightweight and strong, and therefore provide fuel economy and other benefits. The traditional approaches for attaching acoustic emission sensors to such non-metallic and non-magnetic materials are not effective.
Accordingly, there is a need for improved means for holding or attaching acoustic emission sensors to non-metallic and non-magnetic materials, such as composites and ceramics, during environmental testing of such materials that provide advantages over known acoustic emission sensor holders.